As the development of network communication and digital data transmission has progressed towards higher transmission rates, the differential transmission technique has been widely utilized in several industrial transmission protocols such as Universal Serial Bus (USB), IEEE-1394, low-voltage differential signaling (LVDS), Digital Visual Interface (DVI), High-Definition Multimedia Interface (HDMI), and Mobile Industry Processor Interface (MIPI).
Common mode noise is conducted on all lines in the same direction, and common mode filters can be used to suppress common mode noise on any line on which such noise is conducted. Traditionally, a common mode filter is comprised of components including an iron core and two coils wound around the iron core with the same winding number. When a common mode current flows through the common mode filter, the two coils generate a magnetic flux in the same direction such that the common mode filter exhibits high impedance and can suppress common mode noise.
To address the requirement of portable electronic apparatuses, thin film common mode filters have been developed. The conventional thin film common mode filter includes two coil conductor layers, two lead-out electrode layers, a plurality of insulation layers, and two magnetic layers. Each coil conductor layer includes a coil, and the two lead-out electrode layers are used to extend the inner ends of the two coils to an edge of the thin film common mode filter for an external electrical connection. Several insulation layers are used for electrically insulating the coil conductor layers and the lead-out electrode layers. The coil conductor layers, the lead-out electrode layers, and the insulation layers are disposed between two magnetic layers. However, after completing the fabrication process, the filtering band of the conventional common mode filter is fixed and cannot be expanded. To meet the requirements of a new filtering band, a redesign and re-fabrication process are needed.
This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.